Permo-Carboniferous paleogeography and coal accumulation and their tectonic control in the North and South China continental plates

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Permo-Carboniferous strata in North China and South China were essentially controlled by paleogeography, paleoclimate and plate tectonics. During that time, North China and South China were separate microcontinents, located on opposite sides of the equator. Thus, the characteristics of their coal deposits differ substantially. In North China the coal seams were initially deposited on a north-sloping epicontinental basin during the Middle Carboniferous. By the middle of the Late Permian, the locus of coal formation had shifted from the north to the south as a result of the uplift of the northern margin due to continental collision with the Siberian plate. As the paleoplate was situated in the low northern latitudes, moist tropical climate and favorable geographic setting allowed the extensive development of Late Carboniferous and earliest Permian peat swamps on the northern alluvial-fluvial plain and central paralic regimes. More significantly, two thick coal sequences were formed in the transition belt between the alluvial apron and fluvial plain and the shoreline area where high groundwatertable fed by both rainwater and groundwater favored the formation of thick peat in swamps. With northward drift, the paleoplate entered the subtropic semiarid and arid climatic belt between the late Early Permian and early Late Permian. Coal formation was restricted to the paralic delta plain where, locally, oceanic wet climate and high groundwatertable prevailed. Following this, the subduction of the Paleo-Tethys beneath the southern margin of North China led to the upwarp of the southern Margin, and kept the delta system growing vertically for a considerable period so that it kept pace with shoreline fluctuations on the southern area. The result was that multicycle deltaic coals were well developed at this stage. In South China, coal was formed in the coastal zone of an epeiric and shelf sea which connected the marinal basins. The basins were frequently influenced by plate-marginal tectonic movements and continental rifting related to back-arc extension. As a result, coal formation was often interrupted by sea-level fluctuations. Early Carboniferous coal was deposited during the short regressions during the widespread transgression, mainly on the restricted marine paralic plain where clastic deposition was active. In the Middle and Late Carboniferous, no coal was formed, because the paleoplate had drifted into a subtropic arid belt. Early Permian coal accumulated at first in the northeast and later in the southwest due to tectonic influences. In the Late Permian, relatively thick and extensive coal was formed, even though it was during a transgressive period in both the western and eastern margins under the equatorial hot humid conditions. In general, the seam geometry and quality (particularly ash and sulfur) of the coal was directly controlled by the geography and the changes in the depositional environments. However, the fluctuation in coal formation and the migration of thicker coal zones was indirectly controlled by paleoclimate and the sea-level fluctuations, in response to plate-tectonic influences.